Help me identify a vampire movie

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I remember I've seen one vampire film as a kid and then never heard about it again. I remember only a bits form it. I think it was children movie but it was pretty damn dark. There was a boy that was hanging out with a vampire. The boy had also a female friend and they were researching something (possibly related to murders or vampires). I remember that this main vampire saved the boy from another vampire on the cemetery but it was staged since in the end the vampire betrayed him and kidnapped the girl and I remember that they were at subway at the end of the movie. Then when the train came out of the tunnel on the sun, all the vampires exploded. The movie has to be at least 10 years old. Ring any bell?